Which HID lighting works best? MH or HPS?
 

I'm new to orchid growing. I understand that HPS is supposed to be better for flowering, but MH is better for vegetative growth. Which works best year round for orchids?

Also, do the more expensive grow bulbs that claim to have a fuller spectrum work and are they worth it?

Depends on if you are supplementing or using it as primary lighting. HPS is probably somewhat more efficient, but I don't think I'd use it as my only light source. It also is less than pleasant to look at, very yellow. I've had good luck with MH lights as a light source in a basement with no external light (although that was 8 years ago).

You get what you pay for. I'd get MH bulbs with the widest spectrum possible. For pure efficiency, you could consider LED lighting. I've been using it with good effect. It isn't pretty to look at though.